Red blood cells from people with hereditary spherocytosis (HS) appear to have abnormal surface membranes which result in the formation of spherical, osmotically sensitive cells that are prone to fragmentation in vivo. It is possible that this membrane instability is due to a defective cytoskeleton composed of spectrin, actin and several other membrane proteins, including bands 2.1, 3, and 4.1. A search will be made for possible structural differences in spectrin extracted from HS cells by analysing intermediate-size peptides and total proteolytic digests by two-dimensional isoelectric focusing - SDS-PAGE, high resolution peptide maps, and high pressure liquid chromatography. The capacity of individual spectrin subunits and peptide fragments to undergo reversible denaturation will be compared with spectrin from normals. If differences are found in HS peptides they will be analysed further by amino acid sequencing techniques. HS spectrin will also be analysed for possible functional differences by studying its capacity to bind to membrane receptors, its capacity to undergo dimer-tetramer transitions, and its capacity to form non-covalent associations between subunits. Interactions of HS spectrin with other cytoskeletal proteins (2.1, 4.1, actin) will also be analysed by non-denaturing PAGE and electron microscopy. Comparable studies of other cytoskeletal proteins from HS cells may also be carried out if no structural or functional differences are detected in HS spectrin.